Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 240715

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
215 AM CDT SAT SEP 24 2016

229 PM CDT

Through Saturday...

A cold front, now stationary, was shoved south through the area today
 by strong high pressure centered across western Ontario. The
high will move southeast towards Lake Huron tonight, which should
help to keep the area locked in cool and moist southeast flow off
the lake. This will keep a low level inversion in place to keep
the stratus locked in or allow it to fill back in for much of the
night into early Saturday. We are seeing some clearing this
afternoon for our southern and western areas. Expect with some
heating occurring in the cloud breaks that there could be some
expansion of the clearing/lifting. Another mild night is expected
with lows in the 60s.

On Saturday the upper ridge will build overhead, and the low level
flow component should shift to more east-southeast. This should
generally allow for more and earlier clearing on Saturday as
opposed to today, though it will be slower-going in northern
Illinois and close to the lake in northeast Illinois. Expect only
modest temperature recoveries from today as well, but the airmass
is still fairly mild as average highs for mid to late September
are in the low 70s. We should see 70s northeast to the mid 80s
across Central Illinois.



244 PM CDT

Saturday night through Friday...

Unseasonable warmth remains possible through Sunday, then a cold
front will bring cooler and more seasonable temperatures back to
the region.

Saturday night into Sunday, strong upper ridge will still be in
place across the western Great Lakes region while an upper low
lifts from the northern Plains into the upper Midwest. Highly
meridional pattern will transport teens Celsius 850mb temps north
into Hudson Bay while low single digits wrap south into the
central plains. On the warm side of the baroclinic zone, surface
temps for Sunday will continue to run above normal with some
models suggesting low to mid 80s much of the forecast area.
Remained a little conservative based on the expected cloud cover
for the day which should be mostly cloudy to cloudy. Models
continue to zero in on precip timing on Sunday, favoring the
showers and thunderstorms along the cold front as it passes
through during the afternoon and evening hours. Cannot rule out
spotty showers earlier in the day with very modest elevated
instability in place during the morning and broad mid-level
southwest flow.

Cool down still on track for Monday as a strong shortwave digs
from the Canadian Rockies Sunday into the Midwest Sunday phasing
with the aforementioned upper low resulting in additional
deepening of the surface low and wrapping 2-3C 850mb temps into
the local area. The combination of the tightening pressure
gradient and cold air advection will drive strong winds during the
day Monday and bumped up winds quite a bit now expected sustained
winds peaking around 15 to 20 mph and gusts to around 30 mph. Any
clearing early in the day should quickly fill in with cold air
stratocumulus during the afternoon and evening hours. Expect only
mid 60s for high temps Monday. Precip on Tuesday looks more
favorable to our north under the departing upper low, then dry
conditions look probable for much of the remainder of the week as
surface high builds into the region and upper ridging builds back
into the mid section of the country allowing temperatures to
moderate back towards normal, even above normal late in the week.



For the 06Z TAFs...

1225 am...Only forecast concern this period are cigs. Low mvfr
cigs will continue with ifr cigs possible...especially west of the
Chicago area terminals. Mvfr cigs will slowly lift by mid/late
morning and then should become vfr by early/mid this afternoon.
Fog will also be possible overnight...but generally south and
southwest of the Chicago area terminals.

Northeast winds around 10kts will continue overnight turning a bit
more easterly later this morning with speeds diminishing Saturday
evening. cms



215 am...Large high pressure over eastern Ontario will move east
to Quebec and New England Sunday into Sunday night as low pressure
over the northern plains lifts northeast into Manitoba tonight.
This low will then slowly move across Ontario Monday into Tuesday.
A trailing cold front will move across the western lakes Sunday
night. Easterly winds today will turn southeast tonight and more
southerly ahead of the front by Sunday afternoon. Speeds of 15-25
kts will diminish some later today but then return tonight into
Sunday with perhaps a few higher gusts. Winds will shift westerly
behind the front Sunday night and steadily increase to 30 kts by
midday Monday and with much cooler air spreading across the
region...its possible a period of gales may develop Monday
afternoon and persist into Monday night. Winds will remain strong
into Tuesday before slowly diminishing Tuesday night into they slowly turn more northerly. cms





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